Counting Duplicates In Sub Array and assigning to property-CodePudding

I have an array of objects with a nested array in which I would like to count duplicate occurances and map them to a counter property.

Input Array:

initialArr = [
              {
               id: 99,
               days: [{date: '2022-08-01'},
                      {date: '2022-08-03'},
                      {date: '2022-08-03'},
                      {date: '2022-08-01'}]
              },
              {
               id: 100,
               days: [{date: '2022-08-01'},
                      {date: '2022-08-02'},
                      {date: '2022-08-02'}]
               }
              ]

Expected output array with counter property:

outputArr = [
              {
               id: 99,
               days: [{date: '2022-08-01', count: 2},
                      {date: '2022-08-03', count: 2},
                     ]
              },
              {
               id: 100,
               days: [{date: '2022-08-01', count: 1},
                      {date: '2022-08-02', count: 2},
               }
              ]

What is the best way to go about this? I have tried a couple methods using map and reduce but I'm running into difficulties with the nesting of the arrays. Any help is greatly appreciated!

CodePudding user response：

Working inside to out, start with the days array...

function removeDupDays(days) {
  // this produces { dateString: [{date: 'dateString'}, ...
  const grouped = days.reduce((acc, el) => {
    if (!acc[el.date]) acc[el.date] = [];
    acc[el.date].push(el);
    return acc;
  }, {});
  return Object.keys(grouped).map(date => {
    return { date, count: grouped[date].length };
  });
}

Use that in a function fixes object's days prop

// given an object with a days prop, remove dup days
function removeObjectDupDays(object) {
  return { ...object, days: removeDupDays(object.days) };
}

Map that over the initial array...

const arrayWithoutDupDays = initialArr.map(removeObjectDupDays);